# CVE-2026-21243: Windows Lightweight Directory Access Protocol (LDAP) Denial of Service Vulnerability

CVE-2026-21243 is fixed in 7 products on 1 platform, first by KB5075904, released February 10, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-21243
- Priority: High
- CVSS: 7.5 (Important)
- EPSS: 0.0141
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Vendor exploitability assessment: Exploitation Unlikely
- Published: Feb 10, 2026
- Weakness: NULL Pointer Dereference
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21243

## Description

<p>Null pointer dereference in Windows LDAP - Lightweight Directory Access Protocol allows an unauthorized attacker to deny service over a network.</p>

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Microsoft | Windows Server 2019 | 17763.8389 | [KB5075904](https://patchblox.com/security/data/fix/microsoft/kb5075904.md) | Feb 10, 2026 |
| Microsoft | Windows Server 2019 (Server Core installation) | 17763.8389 | [KB5075904](https://patchblox.com/security/data/fix/microsoft/kb5075904.md) | Feb 10, 2026 |
| Microsoft | Windows Server 2022 | 20348.4773 | [KB5075906](https://patchblox.com/security/data/fix/microsoft/kb5075906.md) | Feb 10, 2026 |
| Microsoft | Windows Server 2022 | 20348.4711 | [KB5075943](https://patchblox.com/security/data/fix/microsoft/kb5075943.md) | Feb 10, 2026 |
| Microsoft | Windows Server 2022 (Server Core installation) | 20348.4773 | [KB5075906](https://patchblox.com/security/data/fix/microsoft/kb5075906.md) | Feb 10, 2026 |
| Microsoft | Windows Server 2022 (Server Core installation) | 20348.4711 | [KB5075943](https://patchblox.com/security/data/fix/microsoft/kb5075943.md) | Feb 10, 2026 |
| Microsoft | Windows Server 2022, 23H2 Edition (Server Core installation) | 25398.2149 | [KB5075897](https://patchblox.com/security/data/fix/microsoft/kb5075897.md) | Feb 10, 2026 |
| Microsoft | Windows Server 2025 | 26100.32313 | [KB5075942](https://patchblox.com/security/data/fix/microsoft/kb5075942.md) | Feb 10, 2026 |
| Microsoft | Windows Server 2025 | 26100.32370 | [KB5075899](https://patchblox.com/security/data/fix/microsoft/kb5075899.md) | Feb 10, 2026 |
| Microsoft | Windows Server 2025 (Server Core installation) | 26100.32313 | [KB5075942](https://patchblox.com/security/data/fix/microsoft/kb5075942.md) | Feb 10, 2026 |
| Microsoft | Windows Server 2025 (Server Core installation) | 26100.32370 | [KB5075899](https://patchblox.com/security/data/fix/microsoft/kb5075899.md) | Feb 10, 2026 |

---

Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.